The present invention relates to a process for machining gears and a machine for performing the same. Numerous types of gear shaving machines are known, by means of which the final machining of gears is performed according to two basic processes. The first process called the "conventional and/or diagonal process" consists of effecting the cutting feed in stages, i.e. the bringing together of the tool and the work-table. The tool and the workpiece are therefore close to one another at the end of each longitudinal stroke or optionally at the end of each alternate stroke of the work-table when the latter is arrested in its longitudinal movement.
In the second process called the "continuous downward feed process", the work-table does not perform a longitudinal stroke and the cutting feed is continuous until the workpiece has approached the tool to the extent necessary for the said workpiece to have in theory the desired dimensions.
Existing machines have devices which permit them to finish gears in accordance with one or other of the processes described hereinbefore or processes derived therefrom, whereby these devices make it possible to pass from one process to the other as required by the user. Generally these machines function on the basis of automatic cycles programmed as a function of the desired degree of finish and obviously of the geometrical characteristics of the gears.
However, it has been found that the existing processes and machines for performing these processes have at least one disadvantage which must be briefly described for the better comprehension of what follows.
When, during the final finishing phase, the tool and workpiece have been brought together by the theoretically desired amount, the taking up of play and the elasticity of the machine members lead to a very slight difference between the desired dimensions for the gear and those which are finally obtained. It has been found that it is necessary to allow the machine and the actual workpiece to "breathe" in order to remove the stresses introduced into all these members during operation. To this end, it has been proposed to move the tool and workpiece a short distance away from one another whilst continuing machining either, for example, by a backwards and forwards pass of the table in the case of the conventional process or by a simple continuation of the rotation of the tool and workpiece in the case of continuous downward feed.
However, this solution has not proved completely satisfactory because the moving apart of the tool and workpiece takes place after these two members have been made to cooperate for machining to the final desired dimensions. Consequently there remains a relatively large tolerance between the desired dimensions and the dimensions finally obtained.